05-单例模式的概念和类型()

单例模式的概念

  • 在程序运行时,同一个类只有一个实例

单例模式的类型

饿汉式

  • public class Singleton {
    private static Singleton instance = new Singleton();
    private Singleton(){}
    public static Singleton getInstance() {
    return instance;
    }
    }

懒汉式

  • class Singleton2 {
    private static Singleton2 instance = null;
    private Singleton2() {}
    public static Singleton2 getInstance() {
    if(instance == null) {
    instance = new Singleton2();
    }
    return instance;
    }
    }

懒汉加锁

  • class Singleton3 {
    private static Singleton3 instance = null;
    private Singleton3() {}
    public static synchronized Singleton3 getInstance()
    {
    if(instance == null) {
    instance = new Singleton3();
    }
    return instance;
    }
    }

懒汉双检锁

  • class Singleton4 {
    private static Singleton4 instance = null;
    private Singleton4() {}
    public static Singleton4 getInstance() {
    if(instance == null) {
    synchronized(Singleton4.class) {
    if(instance == null) {
    instance = new Singleton4();
    }
    }
    }
    return instance;
    }
    }

静态内部类实现单例

  • class Singleton5 {
    private Singleton5() {}
    public static final Singleton5 getInstance(){
    return SingletonHolder.INSTANCE;
    }
    private static class SingletonHolder {
    private static final Singleton5 INSTANCE = new Singleton5();
    }
    }

主要记住饿汉式和懒汉式即可

主要记住饿汉式和懒汉式即可

————————

单例模式的概念

  • 在程序运行时,同一个类只有一个实例

单例模式的类型

饿汉式

  • public class Singleton {
    private static Singleton instance = new Singleton();
    private Singleton(){}
    public static Singleton getInstance() {
    return instance;
    }
    }

懒汉式

  • class Singleton2 {
    private static Singleton2 instance = null;
    private Singleton2() {}
    public static Singleton2 getInstance() {
    if(instance == null) {
    instance = new Singleton2();
    }
    return instance;
    }
    }

懒汉加锁

  • class Singleton3 {
    private static Singleton3 instance = null;
    private Singleton3() {}
    public static synchronized Singleton3 getInstance()
    {
    if(instance == null) {
    instance = new Singleton3();
    }
    return instance;
    }
    }

懒汉双检锁

  • class Singleton4 {
    private static Singleton4 instance = null;
    private Singleton4() {}
    public static Singleton4 getInstance() {
    if(instance == null) {
    synchronized(Singleton4.class) {
    if(instance == null) {
    instance = new Singleton4();
    }
    }
    }
    return instance;
    }
    }

静态内部类实现单例

  • class Singleton5 {
    private Singleton5() {}
    public static final Singleton5 getInstance(){
    return SingletonHolder.INSTANCE;
    }
    private static class SingletonHolder {
    private static final Singleton5 INSTANCE = new Singleton5();
    }
    }

主要记住饿汉式和懒汉式即可

主要记住饿汉式和懒汉式即可